Hi,
I took a closer look at the vega documentation and it seems that signals are updated sequentially. So the behaviour is normal...
Still I managed to do what I wanted by creating the following signal:
{name:"sigrepaintMap",on:[{events:"timer{2000}",update:"setMapView([sigLongitude,sigLatitude],sigZoom)"}]}
setMapView() modifies all three signals at the same time.
The info was found here: GitHub - nyurik/leaflet-vega: Leaflet layer based on Vega visualization grammar.
Regards.